It is known to propel a boat or other watercraft using a water jet apparatus mounted to the hull, with the powerhead being placed inside (inboard) the hull. The drive shaft of the water jet apparatus is coupled to the output shaft of the inboard motor. The impeller is mounted on the drive shaft and housed in a jet propulsion pipe or water tunnel.
To facilitate use of water jet-propelled boats in shallow water, it is known to mount the water jet at an elevation such that the water jet does not project below the bottom of the boat hull. This can be accomplished, for example, by installing a duct in the stern of the boat, the duct being arranged to connect one or more inlet holes formed in the bottom of the hull with an outlet hole formed in the transom. The water jet is then installed outside the hull in a position such that the water jet inlet is in flow communication with the duct outlet at the transom. Such a system is shown in Australian Patent Specification No. 262306, published in 1963. Alternatively, the water jet can be installed inside the duct built into the hull, as shown in U.S. Pat. No. 5,181,868.
In another type of design, a water jet apparatus is installed inside the hull and penetrates the transom. An inlet housing of the water jet has a horizontal opening and an inclined water tunnel for guiding water to the impeller. The horizontal opening of the inlet housing is mounted in a hole in the bottom or near the bottom of the hull. A similar design is disclosed in Swiss Patent No. 481788.
In many water jet units powered by inboard engines, the drive shafts and pump mountings (which must penetrate the hull) are placed below the waterline. This mounting system has the disadvantage that various gaskets and seals are required to ensure the integrity of the installation. Leakage at any of the mounting and shafting locations can be disastrous.
There is a need for a boat design which would allow a water jet apparatus to be mounted to a hull with penetrations for the drive shaft and shift and steering control system. The area of these penetrations through the hull should be minimized. In addition, the mounting arrangement should allow for easier installation than is the case with the above-described prior art mountings.